Many portable electronic devices use a rechargeable battery as a power source. Example portable electronic devices include computers, cellular telephones, pagers, radios, and the like. While there are many types of rechargeable batteries used today, including nickel cadmium and nickel metal hydride, lithium ion batteries have become a popular choice. Lithium ion batteries are typically smaller and lighter than other rechargeable battery types with increased charge capacity.
The charging of lithium ion batteries is conducted in a different manner than the charging of nickel type rechargeable batteries. Generally, nickel-type rechargeable batteries are charged by applying a constant current from a battery charger to the battery until the cell reaches a predetermined voltage or temperature. A lithium ion cell, however, uses a different charging process. First, the lithium ion cell is supplied with a current from a battery charger until the cell's voltage rises above a threshold. Next, the battery charger is held at the threshold until the current of the cell decreases to a predetermined level. Damage to at least the battery or battery charger may occur when a battery charger applies an improper voltage to a rechargeable cell.